1. Field of Invention
This invention relates to an image quality analysis system that obtains consistent image quality measurements regardless of the particular image input device used.
2. Description of Related Art
It is well known that customer satisfaction can be improved and maintenance costs reduced if problems with copiers and printers can be fixed before they become serious enough to warrant a service call by the customer. While current technology exists to enable printers and copiers to call for service automatically when sensors detect certain operating parameters outside of permissible ranges, there is not a very comprehensive manner of detecting incipient system failure or automatically diagnosing when problems with image quality reach a level where human observers perceive a reduction in quality. This is caused not only by the large number of operating parameters that would need to be tracked, but also because these parameters are strongly coupled to one another. That is, a given parameter at a certain value may or may not be a problem depending on the values of other parameters. While existing systems provide some level of image quality analysis, these systems have been found less than satisfactory as image quality determination is machine dependent and may be inconsistent with perceptions of image quality as judged by human users.
Systems which can perform image analysis on printed test samples can be used in a variety of ways to provide solutions and value to users of digital printers and copiers, for example as the analysis engine for automatic or remote diagnosis of print quality problems, or for monitoring quality as part of a print quality assurance system.
The system would typically use an input scanner, either stand-alone or part of a multi-function printer/scanner/copier, to scan the printed test sample, and then perform a series of analyses on the scanned image. Alternatively, a CCD camera could be used in place of the scanner. It is important to have consistent behavior of such systems, when used with different input scanners. That is, the results of the analysis from one input scanner should be essentially identical to results from other input scanners. Only if this is the case, can the IQ measurements from one such system be compared with other systems. In the case where the system is used by the printer/copier user, for example for IQ assurance purposes, it is imperative that the results be consistent in order to compare with industry standard measurements.
However, the input scanner is likely to be part of a multi-function printer/scanner/copier, and each system would therefore use a scanner with different characteristics, especially in terms of spatial resolving power.
This invention overcomes problems with differences in analysis results caused by use of different image input devices by providing a computational process that allows absolute image quality measurements to be performed consistently from scans of print samples, largely independent of the resolving power of the scanner. Absolute image quality metrics reflect quality as seen by a human observer. By determining the resolving characteristics of the input scanner, the scanned image can be processed, with little or no artifacts, to resemble the image as perceived by a human observer, while at the same time eliminating differences that would arise when using a scanner having a different spatial resolving power, provided that the resolving power of each scanner is sufficiently greater than the resolving power of the human visual system.